Commonly assigned U.S. Pat. No. 4,663,685 discloses an MR read head comprising an active central region and passive end regions. Each passive region comprises a respective conductor lead and suitable means for longitudinally biasing the head. A soft magnetic film is separated from the MR layer by a thin spacer layer to provide a transverse bias of approximately 45 degrees in the active central region of the MR layer. Magnetic shields, which are separated by insulating material from the conductor leads and MR head, respectively, minimize the effects of stray magnetic flux that would decrease the resolution of the read back signal. This MR head configuration operates very satisfactorily when very high linear recording densities are not required.
However, the combined thickness of the gap insulation layers and MR element defines the linear bit resolution of the head. Thus, in order to fabricate high linear recording density heads the thicknesses of these gap layers must be substantially reduced. The electrical insulation properties of the gap layers, as deposited, may be adequate to isolate the MR element and shield. However, the thicknesses of these alumina gap layers (which are deposited as very thin films) are reduced by subtractively etching (e.g., ion milling) during patterning of the MR element and by developer etching during photoprocessing to form the conductor leads. The total alumina removed depends upon the degree of overetching that is required to ensure proper pattern definition during these two steps.
It will be apparent that as the initial thickness of the gap layers is reduced to achieve higher linear resolution, the thickness of the alumina thin films that separate the conductor leads from the respective shields can easily become insufficient to provide the necessary electrical insulation. If this occurs, the MR element can be electrically shorted to either or both of the shields and render the MR head inoperable.